Are you one of those people who opt for low-fat dressing on your salad, pour non-fat milk over your cereal, or eat lean cuts of meat or skinless chicken? Many of us choose low-fat options to avoid gaining weight or prevent heart disease. Recent research indicates that these fears are unfounded and that eating low-fat foods could actually increase your risks of developing neurodegenerative disorders such as Alzheimer's.
Alzheimer's disease is growing at epidemic proportions and our fascination with low-fat dieting over the past few decades may have something to do with it. Over 5 million Americans suffer with Alzheimer's. In 1980 Alzheimer's affected less than 0.3 people for every 100,000 in the US. By 2006 that number shot up to 20 per 100,000. The number of cases is expected to double over the next couple of decades. This sharp rise in Alzheimer's is worrying doctors and researchers. "Alzheimer's is going to swamp the health care system," says Dr. John C. Morris, a neurology professor at Washington University in St. Louis and an adviser to the Alzheimer's Association. "It's frightening," says Rachel A. Whitmer, PhD, an Alzheimer's research scientist at Kaiser Permanente in Oakland, California. Alzheimer's is now the seventh leading cause of death in the US.
Alzheimer's is currently one of the most common diseases of the elderly. Although the disease was first identified in 1906, it remained a rare condition until the 1980s when rates began to skyrocket. Prior to 1960 there was almost no mention of the disease in the medical journals. "I looked everywhere," says Murray Waldman, MD an Alzheimer's researcher from St. John's Rehabilitation Hospital, in Toronto, Canada. "I looked on three continents and in every medical library I could find, including the Library of Congress and the British Museum library." Yet, there was little mention of the disease, indicating the rarity of the condition just a few decades ago. "I also looked at psychiatric literature and at the pathology literature, but no matter where I looked, I couldn't find anything that indicated there was very much Alzheimer's disease prior to the 1960s," says Waldman. It might be argued that Alzheimer's was more prevalent back then but nobody noticed it. Waldman says he cannot accept that answer, "because of all diseases, Alzheimer's is one of the most difficult to miss." The only other plausible explanation, he says is that it was far less frequent then than it is now.
What has happened over the past few decades that may have caused this dramatic rise in Alzheimer's?
Alzheimer's usually surfaces after the age of 60. Yet, it can occur as early as the 40s or 50s. Over half a million Americans under the age of 60 have Alzheimer's. While the risk of Alzheimer's increases with age, it is not a part of the normal aging process. It is a disease. The brains of Alzheimer's patients are distinctly different from the brains of those people who age normally.
There is no known cure. Doctors don't even know what causes it. However, the sharp rise in Alzheimer's over the past four decades points to something in the environment as the culprit. The disease is more prominent in industrialized nations than in Third world countries, suggesting the cause is associated with our changing lifestyle. Diet readily comes to mind. Our diet has changed dramatically over the last 40 years. Could diet be the cause or a contributing factor of the emerging Alzheimer's epidemic?
One of the biggest changes that has occurred is the shift from eating foods rich in saturated fat and cholesterol, to eating low-fat, and low-cholesterol foods. Since the 1970s we have been in a low-fat craze. Saturated fat and cholesterol have been purged from the diet. We've switched from eating whole foods rich in natural fats to low-fat and non-fat milks and cheeses, lean cuts of meat, yolkless egg whites, skinless chicken, low-fat this and no-cholesterol that. Everywhere you go, you are offered low-fat food options. Total fat consumption has dropped from about 40 percent of total calories in the 1960s to about 30 percent now. Dietary fat has been demonized so severely that out of fear many people restrict their total fat intake to less than 20 percent. As a result, we have become a fat deficient society.
What has been the result? Obesity is at an all time high. Over 60 percent of Americans are overweight and one-third of the population is obese. While saturated fat and cholesterol intake has dropped dramatically, heart disease is still our number one killer. Other diseases such as diabetes and Alzheimer's are on the rise. Low-fat diets are not working.
It is interesting that as we have moved away from eating fat and cholesterol, the incidence of Alzheimer's has skyrocketed.
Fat is an essential element of the human brain. Sixty percent of the brain consists of fat and cholesterol. While the brain accounts for only 2 percent of the mass of the body, it contains almost 25 percent of the body's cholesterol.1
The cells of our body are encased in a lipid (fat and cholesterol) membrane. Even the individual organelles (cell organs) inside the cell are encased in a lipid coat. Fat provides the basic framework for our cells. Cholesterol is needed for structural support and to regulate the entry and exit of certain hormones, fats, and proteins. Fat and cholesterol are constantly being formed to maintain, replace, and repair the cells and tissues. In order for the cells to function properly, they must have ready access to an adequate source of fat and cholesterol.
Each organ in our body is basically a collection of cells. When an organ isn't functioning properly, the reason for it is because the cells that make up the organ aren't functioning properly. Illness is a cellular condition. When your cells are healthy, your organs are healthy, and when your organs are healthy, you are healthy. The key to good health is to have healthy cells.
A lack of adequate fat and cholesterol in the diet can have a pronounced effect on the health of every cell in the body and particularly on the neurons – the brain cells. The fat we eat influences the amount of fat and cholesterol available to the brain. Our diet can have a pronounced influence on our mental health. Cholesterol, for instance, is essential for the transmission of nerve impulses and for the storing and retrieving of memories. The synapses – the highly specialized junctions between the brain cells – depend on cholesterol in order to transmit signals from one neuron to another.2 Any interference with normal cholesterol synthesis can impair nerve tissue maintenance and repair, leading to neuron degeneration.3 Even a small depletion of cholesterol – less than 10 percent – has been shown to be enough to inhibit nerve transmission.4 When this happens memory and cognitive skills decline.5
A number of studies have shown that the amount of cholesterol circulating in the blood influences brain function. Low blood cholesterol is associated with poor cognitive performance. Higher cholesterol levels appear to improve memory and cognitive skills and protect against neurodegenerative diseases such as Alzheimer's.
For example, researchers at Johns Hopkins University monitored a group of 392 subjects for 18 years. All of the subjects were 70 years of age at the beginning of the study. Every few years the investigators measured their cholesterol levels and conducted cognitive tests. The study revealed that those people with the highest blood cholesterol levels scored the highest on cognitive tests.6
These results were supported by another study from Mount Sinai School of Medicine, in New York. In this study 185 subjects over the age of 84 and without dementia were assessed. Higher total cholesterol and higher LDL cholesterol was associated with higher memory scores on tests. The researchers' conclusion: "high cholesterol is associated with better memory function."7
Researchers at Seoul National University in South Korea came to similar a conclusion. For three years they followed 106 elderly subjects with possible dementia. As with the other studies, those with the highest cholesterol readings performed the best on neuropsychologic tests. Those who eventually digressed into Alzheimer's disease had lower cholesterol readings.8
A study published in the Journal of Biological Chemistry shows that dietary fat and cholesterol, the type found in foods such as eggs and meat, can protect the brain from the physiological changes that are associated with Alzheimer's disease. This study provided evidence that dietary fat and cholesterol improve brain cholesterol status and helps protect against the formation of amyloid plaque, a feature found in the brains of Alzheimer's sufferers.9 This study demonstrated that dietary measures can be taken to help protect against developing neurodegenerative disease. It also suggests that the wrong type of diet (i.e., low-fat) can promote neurodegeneration.
Some people may worry that eating foods rich in fat, particularly saturated fat, will increase their risk of getting heart disease. A recent study published in the American Journal of Clinical Nutrition says this isn't so. Researchers at Harvard School of Public Health and the Children's Hospital Oakland Research Institute pulled together all the studies that have been published over the last couple of decades with data for dietary saturated fat intake and risk of cardiovascular disease. This meta-analysis study included data from 21 previous studies involving nearly 350,000 subjects. The focus of this study was to determine if there was sufficient evidence linking saturated fat consumption to heart disease. Their results said "no." Intake of saturated fat was not associated with an increased risk of heart disease. Those people who ate the greatest amount of saturated fat were no more likely to suffer a heart attack or stroke than those who ate the least. Those people who ate bacon, eggs, and steak every day had no more incidence of heart disease than vegetarians who never touched meat, dairy, or eggs. It didn't matter how much saturated fat one ate, the incidence of heart disease was not affected.10 This study was important because it provided definitive proof that saturated fat consumption does not lead to heart disease.
Low-fat diets are dangerous. They do not protect against heart disease nor do they prevent obesity. They starve the body of the lipid building blocks needed to achieve and maintain healthy brain function, thus lowering cognitive performance and increasing the risk of Alzheimer's. Including good sources of fat in the diet is a smart way to help protect yourself against Alzheimer's.
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2. Pfrieger, F.W. Role of cholesterol in synapse formation and function Biochem Biophy Acta 2003;1610:271-280.
3. Klopfleisch, S., et al. Negative impact of statins on oligodendrocytes and myelin formation in vitro and in vivo. J Neurosci 2008;28:13609-13614.
4. Goritz, C., et al. Role of glia-derived cholesterol in synaptogenesis: new revelations in the synapse-gila affair. J Physiol Paris 2002;96:257-263.
5. Tong, J., et al. A scissors mechanism for stimulation of SNARE-mediated lipid mixing by cholesterol. Proc Natl Acad Sci USA 2009;106:5141-5146.
6. Mielke, M.M., et al. High total cholesterol levels in late life associated with a reduced risk of dementia. Neurology 2005;64:1689-1695.
7. West, R., et al. Better memory functioning associated with higher total and low-density lipoprotein cholesterol levels in very elderly subjects without the apolipoprotein e4 allele. Am J Geriatr Psychiatry 2008;16:781-785.
8. Lee, D.Y., et al. Combination of clinical and neuropsychologic information as a better predictor of the progression of Alzheimer disease in questionable dementia individuals. Am J Geriatr Psychiatry 2006;14:130-138.
9. Howland, D.S., et al. Modulation of secreted beta-amyloid precursor protein and amyloid beta-peptide in brain by cholesterol. J Biol Chem 1998;273:16576-16582.
10. Siri-Tarino, P.W., et al. Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease. American Journal of Clinical Nutrition 2010;91:535-546.